Apparatus for measuring the oxygen consumption of a reducing organic medium

ABSTRACT

Apparatus for the automatic and continuous measurement of the course of the consumption of oxygen, also called the biochemical oxygen demand, of a sample of a reducing organic medium, at a substantially constant oxygen pressure. One of the applications of this apparatus is the study of the biochemical oxygen demand of water polluted by effluents.

United States Patent 1 Courtois et al.

[ 1 Nov. 27, 1973 APPARATUS FOR MEASURING THE OXYGEN CONSUMPTION OF A REDUCING ORGANIC MEDIUM [76] Inventors: Andre Courtois; Yves Lacombe;

Jean Laporte; Georges Kovacsik, all of Nimes, France [22] Filed: Sept. 27, 1971 [2]] Appl. No.: 183,928

- [52] US. Cl. 23/253 R, l95/l03.5 R

[51] Int. Cl. G0ln 33/16, G0ln 33/18 [58] Field of Search 23/230 B, 230 R,

23/230 PC, 232 C, 253, 254; 195/1035 [56] References Cited UNITED STATES PATENTS 3,282,803 11/1966 Poepel et al. 23/230 R X Primary Examiner-Robert M. Reese Attorney-John R. Janes et al.

[5 7] ABSTRACT Apparatus for the automatic and continuous measurement of the course of the Consumption of oxygen, also called the biochemical oxygen demand, of a sample of a reducing organic medium, at a substantially constant oxygen pressure. One of the applications of this apparatus is the study of the biochemical oxygen demand of water polluted by effluents.

6 Claims, 1 Drawing Figure r1 APPARATUS FOR MEASURING ETHE OXYGEN CONSUMPTION OF A IREDUCING ORGANIC MEDIUM The present invention relates to apparatus for measuring continuously the oxygen consumptionof a reducing organic medium during a period that may vary from severalhours to several days.

It is an object of the invention to provide apparatus which allows the total quantity of oxygen consumed during a specific period :by living micro-organisms contained in a given medium,- in particular in pollutedwaters, to be measured and recorded. A further object. of the invention is to allow the course of the oxygen consumption in the course of the period to be followed and, furthermore, to allow this consumption to be studied while preserving a constant partial oxygen pressure in the atmosphere. abovethe medium.

It is knownthat the measurement of the biochemical oxygen demand, currently designated by the initials B.O.D., consists in determining the quantity of oxygen consumed, during a specificperiod by agiven medium,

for example by a liquid, or a soil containing living-micro-organisms. These microorganisms are aerobic bacteria which transformthe-biodegradablerorganic matters contained in the medium-by consuming oxygen. The measurement of the. consumption of oxygen therefore allows a medium, water or soil, itsevolution and its aptitude for self-purification, to'be indirectlystudied.

The, most important and the. most current application of the measurement of the B.O.D. isathestudy of the pollution of water by effluents. The degree ofpollution is determined 'by effecting a measurement of the B.O.D. for a period of'5.days.

The techniques used to date for measuring the B.O.D. havecertain disadvantages-and do not-allow automatic recording.

Techniques employing dilution call forinumerous'dilutions and thenatural .conditionsof oxidation of the organicmedia arenottaken into account, .the quantity of oxygen present in the confined medium diminishing in the course of the measurement.

Techniques employingpressure reduction of depression, inwhich the partial.reductionzinpressure, ordepression, in a sealed. enclosure-duetorthe absorption of oxygen is evaluated,.-entail amodification. ofathe natural conditions.

In fact, thecomposition ofsthe-atmosphere' in contact with the medium studied varies, the partial oxygen pressure diminishingin: the: courseof-the measurement and the total pressure diminishingalso.

In order to remedy the pressure decrease, another technique, employing variation of 'volume is used, which allows the pressure "to-be -reestablished :by progressively reducing the volume. ln this .case, the :decrease in .volume, which corresponds to-thequantity. of oxygen consumed, is measured. However, this technique does notobviatethe variationsiincompositionof v, 60

the atmosphere in .whichctheproportion of oxygen'is diminishing.

This technique necessitates the use .of micrometric screws and allowsonly very small-variations in volume to be compensated-" is appliedto the :measurementof the consumptionofoxygen'by cultures'ofbacteria ina nutritive mediumof reduced volume. lthasnotjbeen applied to themeasurement of the consumption oi oxygen by a reducing organic medium in which the bacteria play the part of a biological'means of oxidation. There is also known a device whichallows the course of the oxygenconsumption as well asthe integrated dosing apparatus which feeds the cell with oxygen, and

an apparatus recording in continuous manner,.as a

function of time, the doses of oxygen injected.

The apparatus in accordance with the invention comprises a container. incapable of passing actinic light and closed by a tight stopper arranged to receive a sample .of the medium whose B.O.D. is desired to be known. A

carbonic gas trap is arranged inside the said container and means are provided for injecting progressively, into the said. container, oxygen contained in a reservoir under constant pressure, in order to re-establish the initial pressure.

Theapparatus further comprises means for measuring the volume-of oxygen injected intothe container,

this measurement corresponding to the biochemical 1 oxygen demand during the periodinquestion.

The apparatus. may also be provided with a differential gaugeconnected to the interior of the said con- .tainer, provided with. a contact whichis connected in 'thefeed circuit of .a motor driving ai pump which appliessuction to the oxygenreservoir and which-dis charges into the said container.

Thegpump may be adosing pump and-the apparatus may include a contact actuated by a cam keyed to the driving shaft of the pump, which contact delivers one pulse during each pump revolution. These pulses can be recorded. graphically or'counted by a pulse counter. Thisrecording allowsthe evolution of the B.O.D. to be evaluated duringthe'course of the measuring period.

In' one advantageous embodiment,:the dosing pump is constituted by .an automatic syringe driven by a motor-which drives a cam acting on the distributing slideof athree-way valve, one waycommunicating with. the syringe, a second communicating with the oxygenreservoir, and'the third-with'the container incapable of passingzactinic'light. The-dosingpump may also be constituted by a peristaltic pump, that is to say a pump constituted by onezormorerollers which squeeze a flexible tube. The oxygen reservoir is preferablyconstituted by a deformable envelope.

Theresults and advantages of apparatus according to the invention are. as follows:

The fact of re-injecting oxygen in order to reestablish continually the initial pressure allows measurementstto beitaken without substantially modifying the conditions of total pressure and of .partial pressure of oxygenin-which-the mediumbeing studied is placed.

Atape-travelling' at aconstantspeed may be used to register the successiveinjectionsof oxygen and this alsince the previously-known systems did not allow this evolution to become known. It explains in fact numerous anomalies and discrepancies which have been detected during the observations hitherto carried out. It also allows the activity of the bacteria to be appreciated during the period of latency due to the adaptation of the germs to the medium, and the lack of activity which is due to a defect in seeding. It also allows the disturbances in the consumption of oxygen due to the precocious activity of the nitrating bacteria to be verified. It permits also a determination of any changes in biochemical oxygen demand as the result of intensive microbiological activity, or of temperatures differing from the usual 20C measuring temperature.

Another advantage of the invention resides in the fact that the pulses which correspond to the injection of each single dose of oxygen can be recorded numerically and the numerical values can enter into information processing units such as a calculator or computer in order to be stored or in order to be used in calculations. For example, it will be possible to establish automatically, from these data, curves showing the course of the consumption of oxygen, the calculations of the corrections due to the seeding, numerical comparisons between samples, etc.

In order that the invention may be more clearly understood, reference will now be made to the accompanying drawing which shows one embodiment thereof, in schematic fashion and by way of example.

Referring to the drawing, there is shown a container 1 which consists of a bottle incapable of passing actinic light and sealed by a stopper 2 provided with a joint 3, such as an O-ring. This bottle is immersed in a bath 26 whose temperature is kept constant, generally at 20C, by a water-cooling system or a Peltier effect system for reduction of temperature and by an electrical heating system for increasing it, the whole being monitored by a thermostat. Into this bottle 1 there is placed a sample 4 of liquid whose B.O.D. it is desired to study. The liquid 4 occupies only a portion of the bottle which is topped up by air at atmospheric pressure.

A chemical carbon dioxide gas trap 5 is placed inside the container 1. This trap is constituted, for example, by a trough containing a concentrated solution of soda or of potash. A magnetic agitator 6 driven by an electric motor 7 is also arranged in the container 1, and a tube 8 passes into the bottle 1 through the stopper 2. Onto a branch of this tube there is connected a differential gauge 9 provided with a contact 10. This contact 10 is wired in series in the feed circuit of a motor 11 which drives a dosing pump. The reference pressure is either the atmosphere or a closed receptacle. The dosing pump shown is constituted by an automatic syringe 12 comprising a cylinder 13 and a piston 14 which is reciprocated therewithin by a connecting rod and crank system 15 articulated on a disc 16 rotated by the motor 1 l.

The syringe 12 communicates through a tube 17 with an oxygen reservoir 18. This reservoir is constituted by a deformable envelope so that the oxygen contained in the reservoir is always at atmospheric pressure.

The syringe 12 also communicates with the tube 8 which leads into the bottle 1. The communications between the syringe, the oxygen reservoir and the container 1 are controlled by a three-way valve 19 having a distributing slide 20 which is operated by a hinged lever 21 actuated by a cam 22 mounted on the disc 16.

A spring 23 exerts on the distributor 20 an action in opposition to that of the lever 21. When the lever 21 is not pushed back by the cam, the spring 23 places the distributor into the position shown in the Figure where the 5 syringe communicates with the bottle. This represents the delivery time of the syringe.

On the other hand, during the time that the cam 22 passes in front of the lever, the slide 20 of the distributor is pushed back and the syringe is in communication with the oxygen reservoir 18. During this same period, the piston 14 moves from top to bottom of the syringe. This represents the suction time of the pump. The volume or oxygen sucked in and delivered into the bottle during each pump revolution is a constant volume at constant pressure corresponding to the volume swept by the travel of the piston 14.

By way of example, the bottle may have a volume of 500 ml, the useful volume of the syringe may have a volume of 1 ml, and the contact of the pressure gauge may be arranged to close when the depression reaches 2 millibars so that the syringe can reestablish the pressure in one stroke. However, by increasing the sensitivity of the differential pressure gauge, the syringe may be arranged to function in steps in such manner that it reestablishes the pressure with minimum discontinuities.

The slide valve 19 may be replaced by spring-loaded suction and delivery valves. The advantage of using a valve of the kind shown at 19, however, is that errors due to the calibration of the springs of conventional valves are avoided.

The apparatus also includes a contact 24 which is actuated by the cam 22 during each revolution of the disc 16 during which time it delivers one pulse. These pulses can be recorded in the form of points inscribed on a recording tape 25 which is caused to travel at a constant speed. The study of the curve formed by these dots supplies information on the evolution of the demand for oxygen during the measurement.

The pulses may alternatively be recorded on a counter so that they may be fed into the store of a computer or other calculator which will be able to use them to effect van'ous processing operations of these bits of information.

Several measuring apparatus may be fed by the same oxygen reservoir and connected to a common multiway recorder.

We claim:

1. Apparatus for the automatic and continuous measurement of the course of the consumption of oxygen of a sample of a reducing organic medium, said apparatus comprising:

a sealed enclosure for receiving said sample;

a carbon-dioxide gas trap located within said enclosure;

a deformable envelope constituting an oxygen reservoir at constant pressure connected to said enclosure; and

means for injecting into said enclosure oxygen taken from said reservoir in order to keep the pressure inside said enclosure constant and to record in a continuous manner, as a function of time, the quantities of oxygen injected.

2. Apparatus according to claim 1, wherein said enclosure is located within a thermostatically controlled enclosure and has walls incapable of passing actinic light.

3. Apparatus according to claim 1, comprising a differential pressure gauge having an electrical contact and connected to said enclosure, a dosing pump arranged to apply suction to said oxygen reservoir and to deliver the oxygen into said enclosure, said pressure gauge having a contact wired in an electrical circuit for feeding a driving motor for said dosing pump.

4. Apparatus according to claim 3, wherein said dosing pump is constituted by an automatic syringe driven by eccentric means, a cam being mounted on said eccentric means to act on the slide of a slide valve having three ways, the first of which communicates with said syringe, the second of which communicates with said oxygen reservoir, and the third of which communicates with said enclosure containing said sample.

5. Apparatus according to claim 3, whrein said dosing pump includes a contact, actuated by a cam during each cycle of said pump, and means for graphically recording pulses corresponding to the opeations of said contact on a record carrier which is moved at a constant speed.

6. Apparatus according to claim 5, further comprising a counter for recording said pulses corresponding to the operations of said contact. 

2. Apparatus according to claim 1, wherein said enclosure is located within a thermostatically controlled enclosure and has walls incapable of passing actinic light.
 3. Apparatus according to claim 1, comprising a differential pressure gauge having an electrical contact and connected to said enclosure, a dosing pump arranged to apply suction to said oxygen reservoir and to deliver the oxygen into said enclosure, said pressure gauge having a contact wired in an electrical circuit for feeding a driving motor for said dosing pump.
 4. Apparatus according to claim 3, wherein said dosing pump is constituted by an automatic syringe driven by eccentric means, a cam being mounted on said eccentric means to act on the slide of a slide valve having three ways, the first of which communicates with said syringe, the second of which communicates with said oxygen reservoir, and the third of which communicates with said enclosure containing said sample.
 5. Apparatus according to claim 3, whrein said dosing pump includes a contact, actuated by a cam during each cycle of said pump, and means for graphically recording pulses corresponding to the opeations of said contact on a record carrier which is moved at a constant speed.
 6. Apparatus according to claim 5, further comprising a counter for recording said pulses corresponding to the operations of said contact. 